Inductive proximity sensors can be employed to provide non-contact detection of an object or target. Such sensors can be utilized for a variety of sensing functions in connection with industrial plants and/or machinery. For instance, inductive proximity sensors can be employed in connection with material handling systems, robot systems, assembly systems and machines, etc. An inductive proximity sensor can emit an output signal when a target enters into a sensing area. Typically, the target is a metallic object such as a ferrous material (e.g., iron, steel, etc.) or other metallic materials (e.g., copper, nickel chromium, brass, aluminum, etc.).
A typical inductive proximity sensor operates by generating a magnetic field from a detection face. When a target moves into the magnetic field, eddy currents swell in the target. The eddy currents, in turn, generate a magnetic field, which interacts with the magnetic field generated by the sensor. In particular, the magnetic field generated by the eddy currents operates to dampen the magnetic field generated by the sensor. The sensor detects the dampening of the magnetic field and triggers an output signal which indicates that the target is in proximity to the sensor location.
Inductive proximity sensors, when employed in an industrial process control and automation systems, can be an integral part of the automotive industry, heavy machinery operations, mining operations, and/or other endeavors where safety and reliability are vital. Such operations employ dangerous equipment capable of causing serious injury to operators and/or other equipment if not maintained in a safe operating condition or state. The International Electrotechnical Commission (IEC), a standard organization, prepares and published international standards related to electrical and electronic technologies such as, but not limited to, power generation technology, transmission and distribution of power to home appliances and office equipment, semiconductors, fiber optics, batteries, solar energy technology, nanotechnology, marine energy technology, etc. For instance, IEC 60947-5-2 relates to proximity devices and IEC 60947-5-3 relates to proximity device with defined behavior under fault conditions. In addition, the IEC publishes safety related standards such as IEC 61508, “Functional Safety of Electrical/Electronic/Programmable Electronic Safety—Related Systems.” IEC 61508 is a product-oriented functional safety standard, wherein human safety is a primary focus. The standard can provide guidance to promote protection of human life through analysis of products, machinery, and/or equipment that can endanger human safety. Moreover, the standard can facilitate minimizing risk in non-safety critical environments as well as protecting valuable machinery or equipment. In particular, IEC 61508 relates to functional safety, which is a part of overall safety that depends on a system or equipment operating correctly in response to inputs. Functional safety is achieved when all safety functions that comprise a safety system are carried and an associated performance level required for each function is met.
Equipment under control can be a set of equipment, machinery, apparatus, plants, or other devices employed for manufacturing, processes, transportation, medical operations, etc. When a foreseeable action or inaction can lead to hazardous events arising from the equipment under control, one or more safety functions can be implemented to maintain a safe state for the equipment under control. The safety functions can be included in a safety system, which includes a plurality of hardware and software components to carry out the safety functions. For a given safety function, a safety integrity level (SIL) can be determined. The SIL is a measure of safety system performance and can be based upon a probability of a failure over time of the safety function. As described in IEC 61508, there are four SIL levels: SIL 1 to SIL 4, with SIL 4 being the highest safety level. However, SIL 3 is considered the highest level of risk reduction achievable with a single programmable electronic system.
Inductive proximity sensors can be employed in safety systems as part of one or more safety functions. For example, inductive proximity sensors can be utilized to detect potentially unsafe conditions such as an object out of position, an obstruction, unsafe distances between objects, and the like. An SIL level applies to an entire safety function (e.g., all hardware and software components implementing the function), as opposed to individual components (e.g., logic controllers, sensors, final elements, field devices, etc.). However, individual components can be designated as suitable for a particular SIL level. For instance, a sensor can be designated as a SIL 3 suitable if, when employed properly, the sensor can facilitate achieving an SIL 3 rating for a safety function. Typical inductive proximity sensors employ a single coil design with a frequency-pulse-timing method. To be SIL 3 suitable, a certain level of test coverage is required. It can be cumbersome to prove testing of a single channel inductive proximity sensor which is sufficient to garner a SIL 3 rating.